Solid freeform fabrication (SFF) is a known technique for manufacturing solid objects, for example by the delivery of material and optionally energy to specified points in space to produce the solid object. Typically, the object is built in layers corresponding to virtual cross sections of the object from a CAD model.
One of the methods for SFF includes 3-D printing.
In U.S. Pat. No. 6,259,962 entitled “Apparatus and method for three dimensional printing”, assigned to the common assignee and incorporated herein by reference in its entirety, describes an apparatus and a method for 3-D model printing. U.S. Pat. No. 6,259,962 describes an apparatus including a printing head having a plurality of nozzles, a dispenser connected to the printing head for selectively dispensing interface material in layers and curing means for optionally curing each of the layers deposited. The depth of each deposited layer is controllable, by selectively adjusting the output from each of the plurality of nozzles.
Typically, the 3-D object is formed on a tray, which may be movable in at least a direction perpendicular to the building plane (Z direction). To reduce cost and maintenance expenses, some systems as described for example in U.S. Pat. No. 6,259,962, include a printing head with dimensions that are shorter than the dimensions of the tray or object and performs sequential raster scanning of the tray, one pass after the other, to form each of the layers.
U.S. Patent Application Publication No. 20050104241, entitled “Apparatus and method for three dimensional model printing” assigned to the common assignee and incorporated by reference in its entirety, describes an object correcting apparatus to alter the thickness of a layer of the dispensed material to a pre-determined height. The object correcting apparatus may include, for example, a roller and a cleaning apparatus to remove material from the roller. The roller may operate at selected speeds and directions, and may be heated and/or cooled, to help in effectively altering dispensed material.
According to embodiments described in U.S. Pat. No. 6,850,334 and U.S. Patent Application Publication No. 20050104241, the 3-D printing systems may include a printing head having a dispensing unit with a plurality of nozzles through which material may be selectively dispensed, a roller unit for removing surplus material from each layer and a curing unit for curing the interface material of each layer to form the 3-D object. The roller unit may include a roller for leveling the material as well as a scraper and trough for scraping and collecting excess building material off the roller. The roller unit in this case is conformed to the dimensions of the printing head.
Typically, the printing head may be movably supported on a plane parallel to the building plane. The printing head is advanced along a printing direction (X direction) to print each pass and then shifted along an indexing direction (Y direction) to print subsequent passes, substantially on the same plane. The roller is rotatably engaged on the printing head such that its longitudinal axis is parallel to the indexing direction and rotates in a direction “opposite” to the direction of printing due to the friction between the roller and the surface. Typically, a motor engaged on the roller, facilitates rotation of the roller.
Typically during raster scanning printing, the printing head dispenses material over a pass, levels that pass with the roller to remove any surplus material over that pass, and then cures that pass. This process is repeated for each pass and over all the layers until the 3-D objects are completed.